1. Field of the Invention
This invention relates to a light-emitting device wherein an electrochemically luminescent material exhibiting electrochemical luminescence (ECL) is employed.
2. Description of the Related Art
The display to be employed in a mobile telephone or a notebook personal computer is required to be thinner and lighter. A display device fundamentally constituted by a luminescent display such as a liquid crystal display and an organic electroluminescent (EL) display is popularly utilized in various fields.
The phenomenon of electrochemical luminescence (ECL) is now attracting much attention as a different light-emitting phenomenon. In this phenomenon, the electrochemical oxidation-reduction of a light-emitting material is produced as a voltage is applied between the electrodes to generate ion radicals, which are then brought into an excited state through the impingement among them, this excited state being subsequently deactivated to cause the emission of light. Since the light-emitting material is dissolved in liquid, even if the light-emitting material deteriorates, it is enabled to diffuse in the liquid so that the light-emitting material can be prevented from being localized. Therefore, it may be possible to avoid producing the prominent difference in deterioration of display performance between neighboring pixels that may become a serious problem in the case of an organic EL display. Further, the electrode material to be employed in this case is not limited to any special materials but may be selected from various materials which are relatively stable.
In JP-A 2007-12566 (KOKAI), there is proposed a light-emitting device which emits a pseudo-white light exhibiting a high illumination intensity. In this light-emitting device, a couple of emission cells, each constituted by a light-emitting layer containing a specific kind of fused-salt electrolyte and a luminescent pigment and by a porous layer, are laminated one another, thereby making it possible to obtain the pseudo-white light. Further, it has been generally tried to realize a white emission display through a combination of a blue emission and a yellow emission.
However, in the case of the light-emitting layer of ECL, the light-emitting material deteriorates because of the application of a voltage thereto. Especially, in the case of the supporting salt incorporated in the light-emitting layer, when the concentration thereof is decreased, it would become impossible to maintain the same degree of luminance unless a higher voltage is applied thereto.